The biosynthesis of pteridines that occur naturally in bacteria and animals will be studied by investigations of the individual enzymes involved and the reactions they catalyze. Specific source materials for these enzymes are Escherichia coli and the fruit fly, Drosophila melanogaster. The function for L-threo-neopterin in E. coli will be studied. This compound is known to be synthesized by E. coli, and we have recently isolated mutants that have an absolute requirement for this compound. Investigations on the enzymatic synthesis of riboflavin from its precursor, GTP, will be continued with the use of bacteria that produce relatively large amounts of this vitamin. The enzyme that catalyzes the decarboxylation of aspartic acid to yield Beta-alanine will be purified from extracts of E. coli and its properties will be studied.